Stressed States and Self-Organized Structuring of W/C Multilayers
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Stressed States and Self-Organized Structuring of W/C Multilayers D.C. Meyer, A. Klingner, T. Leisegang, Th. Holz1, R. Dietsch1, P. Paufler Institute of Crystallography and Solid State Physics, Dresden University of Technology, Mommsenstrasse 13, D-01069 Dresden, Germany 1 Fraunhofer Institute for Material and Beam Technology, Winterbergstrasse 28, D-01277 Dresden, Germany
ABSTRACT Characterization and quantitative analysis of stressed states of a series of W/C multilayers (10-40 periods prepared by pulsed laser deposition on Si (111) substrates of different thickness) were carried out by means of X-ray reflectometry, wide angle diffractometry and a novel laser mapping device. As the W/C multilayers were dedicated to technical applications as X-ray optics and subjected to optimization of stacking parameters (thickness and number of layers) for a long term (mechanical) stability also further investigations will be discussed. Comparison of wafer distortion as evaluated by laser scanning and strain of the W layer as deduced from X-ray diffraction let us conclude that W layers are under compressive and C layers under tensile stress. The investigation of the thermally stimulated relaxation behavior of the multilayers provided a confirmation of these results. Additional information could be obtained by comparative relaxation experiments under external mechanical constraints. Furthermore, we report on a selforganized process of structuring of the multilayers under investigation, which might be of interest also from a technical point of view. The entire surface area (diameter 2’’) could be converted from the smooth (as-deposited) to a structured (relaxed) state stable at room temperature. Investigations using optical and atomic force microscopy showed that the topology of the surface consists of a mountain range where the valleys are on the level of the as-deposited non-debonded surface and that long wrinkled ridges of about the same height run along arbitrary directions.
INTRODUCTION Mechanical stresses of multilayers are mostly important regarding their mechanical stability. Beyond that, they represent additional enthalpy contributions, which can enable the metastable thermodynamic system represented by a multilayer, to transform to another metastable state toward thermal equilibrium. Thus, all above the thermal stability of the multilayer under stress can be lowered tremendously. The characterized series of multilayers (1040 periods on Si (111) substrates of 300 µm thickness, for a selected series also on substrates of different thickness) was manufactured by Pulsed Laser Deposition (PLD), favorable for the achievement of extended homogeneous layers (for details see [1]). For all samples deposition conditions were kept constant, while stack parameters were varied systematically, in order to correlate the observed distortions unambiguously with the layer parameters and to size up the stressed states quantitatively.
L12.2.1
EXPERIMENTAL METHODS FOR CHARACTERIZATION (i)
Quantitative evaluation of the macroscopic stres
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